Presently, there are several methods of detecting leaks in objects. Some of these methods consist of enclosing the object to be tested in an enclosed, hermetically sealed vessel and exposing the sealed volume to the "tracer" gas, or gas to be detected. Helium is commonly employed as a tracer gas. A mass spectrophotometer, in contact with the atmosphere inside the enclosed volume, is then used to detect any helium. If any helium exists in the test chamber, it is assumed to have leaked from the test object.
U.S. Pat. No. 4,608,866 discloses a leak detector using a cryogenic pump which is kept at a temperature of about 16 K to about 22 K and is in a range to adsorb the nitrogen from the system. There is nothing in U.S. Pat. No. 4,608,866 indicating the present invention's main novel feature which is a cyclic adsorption and desorption of the accumulated helium on a cold non-porous metallic surface between 9 K or lower and 10 K to 20 K after other stages of a cryopump have removed other gases. U.S. Pat. No. 4,608,866 sets forth a leak detection sensitivity up to 10.sup.-12 atm cc sec.sup.-1.
U.S. Pat. No. 4,785,666 is another leak detector but the range for the coldest section is mentioned as 10 K to 22 K. The sensitivity of this invention is set forth as up to about 10.sup.-12 atm cc sec.sup.-1.
U.S. Pat. No. 4,593,530 shows a leak detection system that has an enhanced sensitivity, to 7.times.10.sup.-12 atm cc sec.sup.-1. It discloses the use of multiple surfaces to remove different gases from the vacuum environment by cryogenic pumping such as removing water and carbon dioxide by freezing out in a temperature range of 40 K to 120 K, freezing out nitrogen, oxygen, argon, CO.sub.2, methane, and halogenated hydrocarbons between 10 K and 25 K, and freezing helium, hydrogen, and neon at temperatures between 2 K and 10 K. Also it discloses cryosorptions for adsorbing gases especially He by finely divided charcoal which desorbs the He when warmed to 20 K. U.S. Pat. No. 4,593,530 thus uses a finely divided adsorbent material for adsorbing helium. This is considerably different from the present invention that teaches cyclic adsorption and desorption of accumulated helium from a non-porous solid metallic surface.